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Excellence in Custom Marine Equipment and Propulsion Systems

    Green Technology Showcase:

BENTLEY Marine Ultra-Compact & Lightweight
AEPS- Advanced Electric Propulsion Systems


    Until recent, electric propulsion systems for boats were "Heavy" and "Expensive". BENTLEY MARINE is proud to introduce a new compact and lightweight revolutionary Advanced Electric Propulsion System (AEPS) which is superior in every significant way to traditional propulsion systems.

    The AEPS uses up to 35% less engine room space, less fuel and in most cases one less Diesel engine. This fact, combined with the freedom to mount components virtually anywhere in the vessel provide for additional interior accommodation for any size yachts.

BENTLEY MARINE AEPS – Advanced Electric Propulsion System is comprised by:

1) Compact & Lightweight Water Cooled Electric Motors

2) Mini Reduction Drive Gears for Electric Motors (12in x12in)

3) Generator Choices:
        i) Multiple Variable Speed Generators sets powered by BENTLEY MARINE Aluminum Diesel Engines or;
        ii) Compact Gas Turbine High Speed Generator or;
        iii) Fuel Cell ( depending on specific power requirement and application)

4) Diesel Generator Gearbox (Required only with Diesel Engine powered Generators)

5) ECM- Electronic Control Module

6) Optional: Hi-Power ElectroMechanical Accumulator Unit (a flywheel energy storage device) or Special Batteries.

    The AEPS is divided into two basic parts, the Generator and the Drive. The Generator creates electric power that feeds the Drive. The Drive turns the prop shafts or water jets. Additionally, the system requires some other electric and electronic components, which are compact and lightweight and can be installed virtually anywhere onboard.


    The answer is reliability. The AEPS electric motors and components are build to run either 1 hour or 10,000 hours per year with the same performance. Contrary to conventional propulsion systems, electric components have few, if any, moving parts and are typically built with a TBO (Time Before Overhaul) of over 25,000 hours. Unlike most Marine Electric & Electronic Components which suffer from corrosion, AEPS components are water tight and built to be cooled by salt water.

    BENTLEY MARINE AEPS are covered by a limited 10,000 hour warranty for its electric components, because that is what our suppliers offer us. In salt exposed, outdoor, 24x7 usage, the components used by the AEPS have a failure rate of less than one half of one percent.

Other considerations for choosing BENTLEY MARINE AEPS:

- Better performance than traditional propulsion systems

- Comparable cost to conventional gasoline and Diesel propulsion

- Half of the noise of conventional propulsion systems

- Electric motors are vibration free

- 40% improvement in fuel economy

- 40% less maintenance (no lubrication, less oil changes, longer life of the Diesel engines)

- 5% or more reduction in weight with Diesel generator and up to 75% with Turbine

- 50% or more reduction in installation time

- Total lower cost of ownership for the boat owner.

The AEPS is Modular System:

    The system is basically divided into two parts:

1) The Generator (Diesel engine, Gas Turbine, Fuel Cell)
2) The Electric Drive

    The generator creates the electric power that feeds the drive. The drive, in turn, rotates the prop shaft or water-jets. BENTLEY MARINE AEPS is also very simple to mount, service and repair.


    Unlike traditional generators, the BENTLEY MARINE AEPS uses either:

i) Multiple Variable Speed Generators (alternators) per a single Diesel engine (up to 9), as required;
ii) Single or multiple Compact Gas Turbine High Speed Generator as required; or
iii) Fuel Cell packs of 85kW each, as required.

    Among the several reasons that make this system great for most yacht applications are: redundancy, low weight and flexibility.

    Our 350kW (469HP) variable speed Generator or Electric Motor modules for Diesels weighs only 290 lbs, so in case an unit needs repair, it can be easily replaced without the use of a crane. The 150kW unit measures only 10"x10"x22". Each modular generator combining gear measures 12"x12"(two shown above) and weighs less than 250 lbs. BENTLEY MARINE AEPS combining gear for modular Diesel generators match various models of BENTLEY MARINE lightweight Aluminum Diesel engines (with standard SAE flywheel adapters). The Diesel engine power curves match those of the modular AEPS generators. Gear ratios are also custom built to match the Diesel engines RPM.

    The most important feature of BENTLEY MARINE’s Advanced Electric Propulsion System is that it can operate (depending on equipment and installation) solely on batteries or on advanced energy storage systems such as Hi-Power Electro Mechanical Accumulator Unit (a flywheel energy storage device), thus independent of the generators.

  Hi-Power Electro Mechanical Accumulator

    Unlike traditional generators, the modular AEPS variable speed Diesel generators do not require a constant RPM (typically a multiple of 60 for normal AC generators). The AEPS simply produces more power the faster the variable speed alternators are turned by the Diesel engine.

    When using Diesels as generators, during acceleration, the AEPS computer controls the Diesel RPM via software, detecting the requested load from the yacht’s throttles, the AEPS computer electronically adjusts the Diesel RPM (using fly-by-wire electronic engine controls) several times a second. As the throttles are pushed forward, the Diesel increases its RPM to meet the power required. At zero shaft speed, the Diesel is at idle. At top speed, the Diesel is at top speed. One throttle forward and one aft produce the same effect. According to BENTLEY MARINE Diesel experts, the AEPS should increase the life expectancy of the Diesel engines, because the torque load is more evenly applied than if was used to turn a propeller.

    The AEPS software also controls the minimum forward and reverse prop shaft speed. It can be easily programmed for virtually any type of Diesel/horsepower/vessel combination in just a matter of minutes, using a standard PC. Once the program has been finalized, it is transferred into the AEPS control system and never needs modification again, unless different propellers or water jets are refitted. Field modification is easy and requires only a laptop computer.

    Since the Diesel engine containing the variable speed generators does not have to be aligned with the prop shafts, transversal mounting can be used as required.


Compact Variable Speed Generators, Electric Motors & Electronic Control Module

    BENTLEY MARINE AEPS variable speed generators produce very high voltage power (460 volts), which is than converted to be used onboard by appliances and electronics.

A few other notes about the Variable Speed Generators:

- Multiple Diesel engines can be used and controlled if the design of the vessel calls for it.

- The Diesels do not have to be identical, so combinations of large and small can be used.

- It is practical to connect up to nine generators to a single Diesel. This would provide total electrical power up to 1800 horsepower

- The generators are completely air/water tight The generator cases are marine grade, anodized aluminum

- The generators are cooled by sea water from the central AEPS cooling pump. All sacrificial zinc is included in this cooling system

- Although the generators and their gearboxes are practically silent, they can be covered by a sound shield without effecting cooling or performance

- The gearboxes are 98% efficient

- The generators are 96% efficient

- The gearboxes and generators are maintenance free. All gearbox lubrication is lifetime.

The Drive (Electric Propulsion Motor):

    An AEPS drive is composed by one or more electric motors interconnected by gearboxes. The gearbox contains the reduction gears and thrust bearing required for the system. AEPS gearboxes do not contain a reverse gear, as the electric motors can be reversed electronically.

    The very smallest AEPS contains a single electric motor attached to the gearbox. The custom systems can contain up to three electric motors per gearbox. This allows the AEPS flexibility in stocking systems and spares and gives the yacht great redundancy. The drawing below shows multiple electric motors combined to turn the same prop shaft.

This picture shows a twin AEPS electric drive configuartion with the combining gearbox.
The Electric Motor Gearbox is angled, so that the motors appear in a 'V' shape.

About the AEPS Electric Motors:

    In order to fully appreciate BENTLEY MARINE’s AEPS, a basic understanding of electric motors and their comparison to tradition gasoline or Diesel propulsion power should be reviewed.

    First of all, electric motors are rated entirely differently than their internal combustion counterparts.

    An electric motor is rated in continuous horsepower while internal combustion engines are rated at peak. The term continuous is very important because in a vector motor, the type that AEPS uses, continuous means across the RPM band. A 133 HP AEPS motor can apply 133 HP at 10 RPM, at 500 RPM and at 3600 RPM. Since torque is computed using horsepower and RPM, an AEPS motor can deliver enormous amounts of torque at very low RPMs.

    Diesel engines have very flat torque curves and can also apply high levels of torque at low RPM, but the restriction of idle speed limits that amount of prop cup that can be used to take advantage of this. This has lead to trolling valves and owners of large vessels trying to dock using just one motor. Again, this is not a problem with the AEPS because our minimum RPM is 10, not 600.

    Therefore, the AEPS can take advantage of using special propellers, such as BENTLEY MARINE anti-cavitating Super Propellers that have much more thrust and efficiency at lower RPMs.

    The AEPS simply puts its horsepower and torque right when you need it! Another important consideration is the RPM range that an electric motor can generate its horsepower. The AEPS electric motors can generate the same exact HP from 4000 through 7000 RPM. This gives electric motors the advantage of being able to use greater reduction gears than conventional Marine engines, resulting that for each reduction, torque is doubled.

    Electric motors have several other ratings; the following is a summary:

    Peak horsepower is typically rated as what the electric motor can do for 1 minute in average conditions. As an example, the AEPS 133 HP electric motor can actually generate 201 HP for about 1 minute without any damage. Peak horsepower is not used as calculation for any BENTLEY MARINE AEPS.

    Service Factor is what the electric motor can output (in HP) if life span in not an issue. BENTLEY MARINE AEPS drive motors have a service life of 50,000 hours before overhaul (TBO). A 133HP motor can be operated at a 120% service factor (160 HP) if the electric energy is available. Operating the motor at this service factor thus, reduces the TBO of the unit significantly and shall be avoided.

More about BENTLEY MARINE AEPS Electric Motors:

- All BENTLEY MARINE electric motors are advanced permanent magnet axial gap synchronous motors.

- It is practical to connect up to nine 150kw motors to a single shaft or four 350kW motors per shaft. This would provide total electrical power up to 1800 electric horsepower per shaft, enough to power a yacht requiring about 4000HP of conventional Diesel propulsion.

- The motors are completely air/water tight.

- The motor cases are marine grade, anodized aluminum.

- The motors are cooled by seawater from the central AEPS cooling pump.

- The motors and their gearboxes are practically silent.

- The gearboxes are 98% efficient.

- The motors are 96% efficient.

- The motors and their gearboxes are maintenance free. All gearbox lubrication is lifetime.


    BENTLEY MARINE AEPS require fewer man-hours to install than any conventional propulsion system.

    The variable speed Diesel Generator system comes with an adjustable frame. Mount the Diesel onto the frame, connect the SAE standard flywheel coupling, attach the gearboxes, bolt on the generators and lower the entire assembly into the engine room. Wiring, hoses, muffler and other items will obviously have to be installed and connected, but the AEPS requires no change to these tasks when compared to a standard Diesel engine installation. The wiring harness and cooling system all come with the system. Our experience has shown that each generator takes 20 minutes or less to wire and connect cooling. Each Generator gearbox requires an additional 10 minutes to connect cooling.

    The Drive system comes with a standard bracket mounting system that allows for 3-plane adjustment. A laser based measurement tool is used to "sight" the gearbox mounting for shaft alignment. Shaft angle is no longer a problem because the entire AEPS drive mounts at the same angle as the prop shaft. Only seven inches of clearance between the shaft and the hull of the boat is required. Stringer widths between 20 and 38 inches can be accommodated. Once the gearbox mount has been sighted, bracket mounts are drilled, through bolted and secured. The gearbox is then lowered and attached to the brackets. The prop shaft is then secured to the gearbox, centered and secured. Electric motors are then bolted onto the gearbox, wiring and cooling attached and the process in complete. In our experience, the entire process takes less than 2 hours per shaft.

    There are other electric and electronic items unique to the AEPS that must also be installed, but their flexibility, space requirements and other considerations are minimal and the AEPS can be installed in less than half the time used on traditional propulsion systems.

More about the AEPS installation:

    Only one thru-hull is required for our cooling system. The AEPS does require a special prop-shaft. The forward end must be a tapered, keyed shaft to specifications. The specially designed shaft adds less than 10% to the cost of a conventional shaft.


    BENTLEY MARINE AEPS is designed and built to weight less than conventional gasoline or Diesel propulsion system of similar torque, performance and range. The final weight of the AEPS system will be determined by the type of generators (Diesel / Turbine /Fuel Cell) and backup energy storage systems used.


How do you compute the needs of your vessel to our system?

    A very simple formula can be used, assuming that you know how much internal combustion horsepower you need for the boat in either gasoline or Diesel power:



    For a gas-powered boat, add the peak rating of both engines together to equal SHP (Shaft Horsepower) and then use the following formula:

(SHP * .5) * 1.1 = SEHP (Shaft Electric Horsepower)


For Diesel-powered boats, the same formula applies, but using a different factor:

(SHP * .65) * 1.1 = SEHP (Shaft Electric Horsepower) Add either amount of kilowatts needed to run the house:

TEHP = SEHP + ((max.house kW * 1.1) * .76)

Example 1: Twin 410 HP Gasoline 502 MPI with a 10kW house generator:

Shafts require: (820 * .5) * 1.1 = 451 SHP

House requires: (10 * 1.4) * 1.2 = 17 HP

Generator motor should be 468 TEHP (total electric horsepower)

Example 2: Twin 340 HP Diesel with a 10kW house generator:

Shafts require: (680 * .65) * 1.1 = 442 HP

House requires: (10 * 1.4) * 1.2 = 17 HP

Generator motor should be 459 TEHP

    For variable speed Diesel generators, match the amount of Total Electric Horsepower up with the AEPS model chart below:




BM-AEPS - 130

65 (86)


BM-AEPS - 170

85 (113)


BM-AEPS - 260

130 (172)


BM-AEPS - 340

170 (226)


BM-AEPS - 390

195 (259)


BM-AEPS - 510

255 (339)


BM-AEPS - 600

300 (400)


BM-AEPS - 700

350 (469)


BM-AEPS - 800

400 (532)


BM-AEPS - 1000

500 (665)


BM-AEPS - 1200

600 (798)


BM-AEPS - 1400

700 (938)


BM-AEPS - 2100

1050 (1407)


BM-AEPS - 3500

1350 (1809)



    Vessels equipped with BENTLEY MARINE AEPS enjoy better performance than traditional gasoline or Diesel inboards, while using less horsepower based upon five very simple facts:

1.The modular electric motors do not require marine gear. Depending on the AEPS, this results in savings between 1 and 10%.

2.Our systems are rated under full load, with no loss due to conditions such as operating temperature, engine wear, fuel quality and others. If you purchase a 400 HP electric system, it will deliver 400 HP during the first hour of use and on the 1000th hour of use. This results in savings of 15% for gas and 10% for Diesel.

3.Our systems produce more low RPM torque than Diesel engines. Countless comparisons and studies have been performed that show that you can use 15-20% less Diesel HP than gasoline HP for the same performance. Our systems require even less HP because our torque curve is so positive.

4.Our systems are lighter (wet weight) by 5% or more (up to 75% with Gas Turbine Generators).


   NEW: All BENTLEY MARINE Aluminum Diesel engines can be ordered with new ultra compact and lightweight variable speed computer-controlled Gensets of 65kW, 85kW and 350kW. The units are connected to the engine via the PTO (Power-Take-Off) gearbox. The innovative energy efficient system enables the yacht to automatically shut-down the auxiliary Genset when the main propulsion engines are running, thus saving lots of fuel.

For more information on BENTLEY MARINE Aluminum Diesel Engines and Gearboxes, please contact us.

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